Cylinder deactivation during at least a portion of the combustion process is a proven method by which fuel economy can be improved. With fewer cylinders performing combustion, fuel efficiency is increased and the amount of pollutants emitted from the engine is reduced. A known method of providing cylinder deactivation in a push rod engine is by using a deactivation mechanism in the hydraulic valve lifter.
A hydraulic valve lifter, whether of the deactivating or non-deactivating type, slides reciprocally in an engine bore. The lifter engages a camshaft lobe via a camshaft follower which typically is a roller follower. Unless suitably guided by an anti-rotation mechanism, the lifter may rotate in its bore during reciprocation, thereby undesirably misaligning its follower from the associated cam lobe.
One version of a prior art anti-rotation guide that prevents rotation of a standard (non-deactivation) hydraulic roller lifter is in the form of a flat plate having apertures for receiving the lifter bodies. The apertures are sized to freely permit reciprocation of the lifter in the guide plate and include a flatted portion along each aperture periphery to matingly engage a flatted portion on each lifter body to prevent the lifter from rotating during reciprocation. In the flat plate version, each lifter must first be individually inserted into its respective engine bore. Then, the plate is positioned on the engine, each guide plate aperture receiving a lifter in its proper rotational orientation. Lastly, the plate is rigidly secured to the engine thereby preventing the lifters from rotating during engine operation.
Another version of a prior art anti-rotation guide used to keep the follower of a standard hydraulic lifter in alignment with the cam lobe is disclosed in U.S. Pat. No. 5,088,455. In that version, the guide is used to also “kit” a bank of lifters prior to engine assembly by snuggly gripping a portion of the lifter body via a substantial interference fit across flatted segments of the lifter body. Because the guide snuggly grips each lifter, a significant frictional drag is created between the lifter and guide which can impede hydraulic recovery of the lifter's hydraulic plunger assembly after being drained of oil during shutdown. In some non-deactivation lifters, frictional drag from the interference fit of a gripping guide can be readily compensated for by increasing the size and internal spring force of the hydraulic plunger assembly. However, because of size constraints placed on the deactivation lifter design, this remedy cannot be readily applied to a deactivation lifter assembly.
In addition, deactivation lifters, as known in the prior art, require a specific rotational orientation to mate with a deactivation oil passage in the engine. A single flat on the lifter body for mating with a corresponding flat on the guide would assure proper alignment with the engine oil passage. However, with only a single flat, some amount of anti-rotation protection is lost. Greater anti-rotation protection could be provided via two opposing flats, but this would defeat the orientation preference needed by deactivation lifters as conferred by a single flat.
Finally, anti-rotation guides known in the art, and used with standard hydraulic lifters, are closed-ended, providing only a clearance orifice for the associated push rod to reciprocate through the guide. Such a guide cannot accommodate a deactivation hydraulic lifter having an external spring tower which is substantially greater in diameter than the push rod.
Therefore, what is needed in the art is an anti-rotation guide which accommodates a deactivation lifter and prevents the hydraulic lifter from rotating in its bore during reciprocation.
What is further needed in the art is an anti-rotation guide which minimizes friction and binding between the guide and the deactivation lifter while also retaining the lifter for kitting purposes.